1. Field of the Invention
The present invention relates to a semiconductor device comprising semiconductor diamond, more specifically to a semiconductor device wherein that an electric field to be applied to a channel formed in the interior of the device located between a drain electrode and a source electrode, is modulated or changed by applying a voltage to a gate electrode, thereby controlling a current flowing through the channel.
2. Related Background Art
Diamond is noted as a material applicable to a semiconductor device which is stably operative even under severe circumstances, e.g., at high temperature, under radiation, etc., or is durably operative even at high output.
A reason that diamond is operative at high temperature is its band gap which is as large as 5.5 eV. In other words, an intrinsic range, i.e., a temperature range where carriers of diamond semiconductor cannot be controlled is absent below 1400 .degree. C.
However, when a semiconductor device is intended to be fabricated by using diamond as a material therefor, it has not necessarily been easy to form a self-aligned type semiconductor device by use of an ion implantation technique.
On the other hand, stable operation of a diamond semiconductor device at high temperature has hitherto been realized by an FET (field-effect transistor) including a non-doped layer of diamond disposed under the gate electrode thereof (as described in Japanese Patent Application No. 301684/1987, i.e., Japanese Laid-Open Patent Application No. 143323/1989).
However, the following points should have been considered at the time of the formation of a non-doped diamond layer on a boron-doped diamond layer (active layer).
When the reaction for forming the non-doped diamond layer is conducted in the same reaction chamber as the reaction for forming the boron-doped diamond layer, it is not easy to form a sharp or steep non-doped layer (i.e., a layer having a composition clearly distinct from that of the active layer) on the active layer (i .e., a boron-doped layer). As a result, the non-doped layer disposed under the gate electrode tends to be thicker, and therefore it is not easy to obtain good transistor characteristics.
On the other hand, when a different reaction chamber is employed in order to form a sharp non-doped layer, a trap level tends to be provided between the boron-doped layer and the non-doped layer.
It is preferred that the above-mentioned non-doped layer has a high purity, and is thin and uniform. However, in general, since diamond is not grown in a stepwise manner, the resultant deposited film tends to have an island-like shape. Accordingly, it is not necessarily easy to form a thin and uniform (or homogeneous) non-doped diamond film. When such an island-like deposited layer of non-doped diamond is disposed between the boron-doped layer and a gate electrode, the leakage current from the gate electrode tends to be increased.